The invention relates generally to x-ray tubes and, more particularly, to a textured surface applied to anode components of an x-ray tube.
X-ray systems typically include an x-ray tube, a detector, and a bearing assembly to support the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then transmits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in a computed tomography (CT) package scanner.
X-ray tubes include an anode structure comprising a target onto which the electron beam impinges and from which x-rays are generated. An x-ray tube cathode provides a focused electron beam that is accelerated across a cathode-to-anode vacuum gap and produces x-rays upon impact with the anode target. Because of the high temperatures generated when the electron beam strikes the target, the anode assembly is typically rotated at high rotational speed for the purpose of distributing heat generated at a focal spot. The anode is typically rotated by an induction motor having a cylindrical rotor built into a cantilevered axle that supports a disc-shaped anode target and an iron stator structure with copper windings that surrounds an elongated neck of the x-ray tube. The rotor of the rotating anode assembly is driven by the stator.
Newer generation x-ray tubes have increasing demands for providing higher peak power. Higher peak power, though, results in higher peak temperatures occurring in the target assembly, particularly at the target “track,” or the point of electron beam impact on the target. Thus, for increased peak power applied, there are life and reliability issues with respect to the target.
In general, radiation heat transfer may be improved by treating a surface such that its emissivity is increased. One known technique includes treating the surface by defining a dense array of cavities beneath the surface that are each exposed to the outer surface via respective small apertures that are on the order of, for example, 10 microns in diameter. In such an arrangement, the cavities behave as black bodies and may have an emissivity of essentially 1.0 over their exposed area on the surface. Thus, the overall emissivity of an original surface may be proportionately improved, and the improvement may be quantified by assuming an emissivity of 1.0 over the effective aperture areas of the cavities and by assuming that the remaining surface area, without apertures, has an emissivity equal to that of the original surface. In other words, the overall surface emissivity may be estimated by assuming that the areas of the apertures have an emissivity of 1.0 and by assuming that the remaining areas without cavities have an emissivity of the original surface. Thus, the overall emissivity may be improved by several-fold over a surface having originally a low surface emissivity.
Such a technique may, in theory, be applied to a surface of an x-ray tube target as well. However, in order to achieve the desired black body characteristics as described, typically the cavities applied to the surface have a depth-to-diameter ratio that is approximately 2:1 or greater. And, due to the unique operating environment of an x-ray tube (i.e., high temperature, high voltage, and high vacuum environment), applying such a treatment to a target may result in other negative consequences that preclude such an application therein.
For instance, cavities having a depth-to-diameter aspect ratio of 2:1 or larger on the surface of an x-ray tube target may introduce high-voltage instability problems in an x-ray tube. Because of the high depth-to-diameter ratio, the thin walls of the cavities tend to be friable, or easily fragmented, and may serve as a particulate source. Furthermore, the cavities may also serve to retain solvents or other films that may be introduced during processing of the target. Such deep cavities may act as virtual sources of contaminants, making cleaning very difficult, and possibly introducing a new long-term failure mode into the x-ray tube.
Therefore, it would be desirable to have a method and apparatus to improve the emissivity of x-ray tube target anode components while maintaining high-voltage stability of the x-ray tube in which it is operating, good mechanical integrity, and simplicity in handling.